U.S. Pat. No. 3,740,384 describes an olefin polymerization catalyst comprising the reaction product of a siloxane-diol and an organometallic zirconium catalyst which may be an alkyl, alkenyl or aralkyl zirconium. Representative organometallic zirconium complexes include those containing allyl, methallyl, methylbenzyl or methylene naphthyl ligands.
D. G. H. Ballard et al., Die Makromolekulare Chemie 170, 1-9 (1973) describe the use of catalysts formed from zirconium compounds and silanols. The zirconium compounds used included tetrabenzylzirconium and tetraallylzirconium.
Ballard indicated (in Abstract of Paper No. 562, 23rd International Congress of Pure and Applied Chemistry, Boston, 1971, p. 236) that replacement of allyl and benzyl ligands on the aforementioned zirconium complexes with halogen atoms gives large increases in polymerization activity whereas introduction of other ligands (including cyclopentadienyl) rendered those compounds inactive for polymerization.